1. Field of the Invention
The present invention relates to image scanner apparatuses, and more particularly to drive mechanisms of image scanner apparatuses for achieving improved alignment of optical units used for image scanning.
2. Description of the Related Art
Image scanner apparatuses, including facsimile machines and copier machines, often achieve image scanning of a document placed on a glass platen through reciprocating an optical unit below the glass platen with a wire drive mechanism. In an exemplary image scanner configuration, one or more wires are used to feed drive force from a drive motor to the optical unit. The wires are routed around pulleys disposed within the optical unit, and the ends of the wires are secured on a housing of the image scanner apparatus.
When image scanning is started, the optical unit is required to be placed so that imaging devices disposed within the optical unit are aligned with the document placement baseline defined on the glass platen; however, the image captured through the image scanning often experiences misalignment on the end of the document, or undesirable tilt, due to the misalignment of the optical unit. Avoiding undesirable misalignment and tilt of the image requires proper alignment of the optical unit.
A conventional method for achieving alignment of the optical unit involves adjusting the securing position of the wire to the optical unit, or adjusting the securing position of the end of the wire to the housing, after removing the glass platen.
However, removing the glass platen not only requires troublesome work, but also provides a possibility that dust is introduced into the optical unit; dust may cause undesirable black stripes within the captured image, when dust is adhered to the optical system within the optical unit.
More specifically, several methods for achieving alignment of the optical unit have been proposed.
Japanese Open Laid Patent Publication No. H04-336855 discloses a conventional drive mechanism for an image scanner apparatus, which is illustrated in FIG. 1. The conventional drive mechanism is composed of a support bracket 25 disposed outside of a frame of the scanner apparatus. The support bracket 25 is connected to a wire 30 through a spring 40. The wire 30 is guided by a resistive guide 20. This drive mechanism allows adjusting the wire tension without removing a glass platen.
However, the conventional drive mechanism shown in FIG. 1 also requires removing a document glass platen for aligning the optical unit, because the other end of the wire 30 is positioned in the housing.
Japanese Open Laid Patent Publication No. H11-184019 discloses an image scanner, which is illustrated in FIG. 2. The image scanner apparatus is composed of a skew adjusting plate 55 that provides easy position adjustment of an optical sensor.
The skew adjusting plate 55 is screwed after the position and angle thereof are adjusted along the directions denoted by arrows 56 and 57, for thereby adjusting the length of a wire 50. This allows a mirror table 58 to be placed at a desired position. The position adjustment of the optical sensor is achieved through appropriately placing the mirror table 58.
However, adjusting the position and angle of the skew adjusting plate 55 requires removing a document glass platen. Accordingly, the mechanism illustrated in FIG. 2 also requires troublesome work for adjusting the position of the optical unit, and does not eliminate the possibility that dust is introduced into the optical unit.
Japanese Open Laid Patent Application No. 2001-223843 discloses another image scanner for easily correcting image distortion. As shown in FIG. 3, this image scanner is composed of a wire 120 that allows position adjustment of a carriage 100 along a minor scan direction, denoted by a symbol “Y”. The carriage 100 supports an image distortion-correcting mirror. Both ends of the wire 120 are secured to a wire holder member 130 that is movable along the minor scan direction.
However, the mechanism shown in FIG. 3 also requires removing a document glass plate for achieving alignment of an optical unit, because the wire holder member 130, to which the moving wire 120 is secured, is disposed inside of the housing unit of the image scanner.
Japanese Open Laid Patent Application No. H11-284806 discloses an image scanner apparatus with a wire drive mechanism that allows assembling wires to the wire drive mechanism before assembling guide rails into a housing. The wire drive mechanism also requires removing a glass platen for achieving alignment of an optical unit.
Finally, Japanese Open Laid Patent Application No. H08-137018 discloses another image scanner for easily assembling a wire into a wire drive mechanism. The image scanner disclosed in this document is composed of a pulley positioned outside a housing for routing the wire. However, this pulley does not provide adjustment of the position of an optical unit.